KX3 antenna question: Using 'remote' groundplane and random wire

[Andrew Moore-3]

Forgive me for what may be a silly question, but I've looked through the
ARRL handbook, done the google searches, etc. and haven't found a solution.

At the risk of starting a thread that may be more suitable for an antenna
forum, I'm asking the Elecraft list in hopes that the KX3, KX1 and K1 users
may have had experience here.

I've got two main operating positions: One in an aluminum-skinned trailer
which goes camping, and one in my shack with said trailer parked in the
yard.

For the camping scenario, for ease of use and simplicity, the KX3 sits
inside the trailer with its built-in antenna tuner's ground connected to
the shell of the trailer, and the hot side going to the random-length wire
tossed into the trees. Works great.

For when I'm home in the shack, I'd like to take advantage of the trailer's
metal shell as a ground plane or counterpoise for a random-length wire,
which could be either the same one from the trailer, or a second one in the
trees.

However, most of the random-length antenna solutions I've seen have
involved having the ground plane (or counterpoise) located at the tuner
itself, which in the case of the KX3 means at the KX3 itself, in the shack,
about 100 feet from the trailer.

Essentially what I want to do is to run the signal from the shack out to
the trailer and have the radiator and ground plane "start" (and split off)
there.  However, I'll definitely need the tuner in this scenario, so will
having the tuner be located 100 feet before the split throw it all off, or
introduce imbalances along, say, a coax run from the shack to the trailer?

I get the sense this may be a very basic question but I admit I'm no
antenna expert so I'm asking the gurus.

To keep the noise level down, direct replies may be best, and I'll be glad
to summarize to the group if there's interest.

Thanks,
--Andrew, NV1B
maineware.net
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[Mike WA8BXN]

Hi Andrew,
 
The best solution is to put a tuner in the trailer that automatically tunes
when it senses RF and a high SWR. Several manufacturers make such tuners.
Connecting the random wire to 100 feet of coax and then having the tuner in
your rig do the tuning will result in high SWR in the coax and a lot of loss
 
 
It would be better if you can't add a remote tuner to not use the trailer as
a ground and run your random wire into the shack and provide the best ground
system you can there.
 
BTW, this is probably a question that will be of interest to many others, so
I am posting to the reflector.
73 - Mike WA8BXN
 
 
 
 
-------Original Message-------
 
From: Andrew Moore
Date: 8/26/2012 8:37:43 PM
To: Elecraft
Subject: [Elecraft] KX3 antenna question: Using 'remote' groundplane
andrandom wire
 
Forgive me for what may be a silly question, but I've looked through the
ARRL handbook, done the Google searches, etc. And haven't found a solution.
 
At the risk of starting a thread that may be more suitable for an antenna
Forum, I'm asking the Elecraft list in hopes that the KX3, KX1 and K1 users
May have had experience here.
 
I've got two main operating positions: One in an aluminum-skinned trailer
Which goes camping, and one in my shack with said trailer parked in the
Yard.
 
For the camping scenario, for ease of use and simplicity, the KX3 sits
Inside the trailer with its built-in antenna tuner's ground connected to
The shell of the trailer, and the hot side going to the random-length wire
Tossed into the trees. Works great.
 
For when I'm home in the shack, I'd like to take advantage of the trailer's
Metal shell as a ground plane or counterpoise for a random-length wire,
Which could be either the same one from the trailer, or a second one in the
Trees.
 
However, most of the random-length antenna solutions I've seen have
Involved having the ground plane (or counterpoise) located at the tuner
Itself, which in the case of the KX3 means at the KX3 itself, in the shack,
About 100 feet from the trailer.
 
Essentially what I want to do is to run the signal from the shack out to
The trailer and have the radiator and ground plane "start" (and split off)
There. However, I'll definitely need the tuner in this scenario, so will
Having the tuner be located 100 feet before the split throw it all off, or
Introduce imbalances along, say, a coax run from the shack to the trailer?
 
I get the sense this may be a very basic question but I admit I'm no
Antenna expert so I'm asking the gurus.
 
To keep the noise level down, direct replies may be best, and I'll be glad
To summarize to the group if there's interest.
 
Thanks,
--Andrew, NV1B
Maineware.net
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[Don Wilhelm-4]

Andrew,

I would suggest that you take your KX3 to the aluminum skinned trailer
and tune you antennas on all band segments.  The take you KX3 with KXAT3
into the house shack and do it all over again.  The 100 foot of coax
will make a difference in the tuning.

If all goes well, problem will be resolved and you can use either of the
Elecraft rigs with no problem.

73,
  Don W3FPR


On 8/26/2012 8:34 PM, Andrew Moore wrote:

> Forgive me for what may be a silly question, but I've looked through the
> ARRL handbook, done the google searches, etc. and haven't found a solution.
>
> At the risk of starting a thread that may be more suitable for an antenna
> forum, I'm asking the Elecraft list in hopes that the KX3, KX1 and K1 users
> may have had experience here.
>
> I've got two main operating positions: One in an aluminum-skinned trailer
> which goes camping, and one in my shack with said trailer parked in the
> yard.
>

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[Jim Brown-10]

On 8/26/2012 5:34 PM, Andrew Moore wrote:
> Essentially what I want to do is to run the signal from the shack out to
> the trailer and have the radiator and ground plane "start" (and split off)
> there.  However, I'll definitely need the tuner in this scenario, so will
> having the tuner be located 100 feet before the split throw it all off, or
> introduce imbalances along, say, a coax run from the shack to the trailer?

The coax WILL add some loss, and how much loss will depend both on the
coax and on the degree of mismatch. HOWEVER -- the additional loss due
to mismatch is often much less than many believe. There's an excellent
graph in the ARRL Handbook that shows this.

Some suggestions. First, ALWAYS use BIG coax to minimize the loss. You
don't need a premium coax -- a decent RG8 with a robust copper braid
shield is fine. Second, for both uses of the antenna, I would run coax
from the rig to the aluminum frame at the point of connection, and make
the shield the connection between the rig and the frame. Then simply put
in a decent coax switch to change between the two operating positions.

Third, once the coax to the house is hooked up, check the VSWR without
the antenna tuner, then use the graphs in the Handbook to first
translate the VSWR reading in the shack to the actual VSWR at the
antenna, then use that value of VSWR to see how much additional power is
lost due to the mismatch.  If the loss is particularly high on any band
due to a really bad match, tweak the length of the antenna to improve
it.  Most really bad matches with a long wire are caused by an antenna
that is very close to an exact multiple of half-wavelengths, or by a
dipole that is very close to an exact multiple of a wavelength.  That's
where the 44 ft vertical came from.

73, Jim K9YC
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